Boron removal and measurement in aqueous solutions

ABSTRACT

In one embodiment, the invention relates to a carbon-based boron removal medium with hydroxyl groups and amine group, and in particular, to a method for forming the carbon-based boron removal medium. In a specific embodiment, nitrogen-doped (“N-doped”) graphene oxide is synthesized by a simple two-step process: (1) oxidation of graphite to graphene oxide, and (2) nitrogen-doping (“N-doping”) the graphene oxide to form the amine group. The resultant N-doped graphene oxide can efficiently remove boron from aqueous solutions. In another embodiment, a method of sensing or detecting the presence of boron in an aqueous solution by using a boron sensing medium comprises at least two hydroxyl groups and at least one pyridinic nitrogen or pyrrolic nitrogen or quaternary nitrogen (i.e. pyridoxine, in particular vitamin B6). The boron ions in the solution would form a highly ionized complex, which can cause significant increase in electrical conductivity of the solution, which can then be used to measure the concentration of boron in said solution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of priorities of Singapore PatentApplication No. 10201510400S, filed Dec. 17, 2015, and Singapore PatentApplication No. 10201510403T, filed Dec. 17, 2015, the contents of whichbeing hereby incorporated by reference in their entirety for allpurposes.

TECHNICAL FIELD

The invention generally relates to a carbon-based boron removal mediumwith hydroxyl group and amine group, and in particular, to a method forforming the carbon-based boron removal medium. In various embodiments,nitrogen-doped (“N-doped”) graphene oxide is synthesized by a simpletwo-step process: (1) oxidation of graphite to graphene oxide, and (2)nitrogen-doping (“N-doping”) the graphene oxide to form the amine group.The resultant N-doped graphene oxide can efficiently remove boron fromaqueous solutions. The invention also generally relates to a boronsensing medium and its use in conductometric measurement techniques todetect and measure the amount of boron present in aqueous solutions.

BACKGROUND

Boron is a naturally occurring element in the environment. Its presencecomes mainly in the form of boric acid (H₃BO₃) or borate ions (B(OH)₄ ⁻,B₄O₇ ²⁻, H₃BO₂ ⁻) or salts. Its aqueous solution plays an important rolein many application fields, e.g. in a middle-scale semiconductorfactory, million tons of pure water with ppb (parts per billion) levelof boron is daily consumed during the manufacture process, higher boronconcentration might cause defects due to the p-type dopant insemiconductor chip manufacturing, and leak might happen.

In irrigation water, boron content must not exceed 1 ppm (parts permillion). Its deficiency and excess are harmful to the normal growth ofplants. On one hand, boron deficiency may reduce absorption of calcium,magnesium and phosphorus in the growth and functioning of plants. On theother hand, excess boron can result in dwarfing or death of plants.

For potable water, the World Health Organization (WHO) recommends aguideline concentration of boron up to 2.4 mg/L level in 2011. Increasedboron content causes problems in cardiovascular, coronary, nervous andreproductive systems. It is particularly dangerous for pregnant women totake excess of boron because of the risk of birth pathology.

The concentration of boron is approximately 5 ppm in seawater. Inseawater desalination, reverse osmotic membrane, capacitivedesalination, and electro-dialysis desalination are the most populartechnologies. However, none of them can efficiently remove boron fromseawater due to its small size and uncharged species of boric acid at pH8.4. In this case, additional post-treatment processes are needed toremove boron during the seawater desalination. These post-treatmentprocesses include electrocoagulation, chemical precipitation, ionexchange processes, and liquid-liquid extraction. However, most of thesemethods are inefficient in solutions of low boron concentrations oradjustment of pH is required.

Accordingly, there remains a need to provide for an improved boronremoval medium and method that overcome, or at least alleviate the abovedrawbacks by controlling and keeping the boron concentration within theapplicable limit.

SUMMARY

According to one aspect of the invention, there is provided a method ofremoving or reducing the amount of boron present in an aqueous solution,wherein the boron exists in a form of boric acid (H₃BO₃) or borate ions(B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻) in the aqueous solution. The methodincludes contacting a boron removal medium with the aqueous solution,wherein the boron removal medium includes a carbon-based materialcomprising at least one hydroxyl group and at least one pyridinicnitrogen, or pyrrolic nitrogen, or graphitic nitrogen, or amine group.The method further includes separating the boron removal medium from theaqueous solution.

According to another aspect of the invention, there is provided a boronremoval medium for use in removing or reducing the amount of boronpresent in an aqueous solution, wherein the boron exists in a form ofboric acid (H₃BO₃) or borate ions (B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻) in theaqueous solution, wherein the boron removal medium includes acarbon-based material comprising at least one hydroxyl group and atleast one pyridinic nitrogen, or pyrrolic nitrogen, or graphiticnitrogen, or amine group.

According to yet another aspect of the invention, there is provided amethod of forming a boron removal medium for use in removing or reducingthe amount of boron present in an aqueous solution, wherein the boronexists in a form of boric acid (H₃BO₃) or borate ions (B(OH)₄ ⁻, B₄O₇²⁻, H₃BO₂ ⁻) in the aqueous solution, wherein the boron removal mediumincludes a nitrogen-doped graphene oxide. The method includes oxidizinggraphite to graphene oxide and subsequently doping the graphene oxidewith ammonia.

According to a further aspect of the invention, there is provided amethod of regenerating a used boron removal medium of the earlieraspect. The method includes contacting the used boron removal mediumwith an acid and rinsing the used boron removal medium with deionizedwater.

According to yet a further aspect of the invention, there is disclosed amethod of detecting and quantifying the amount of boron present in anaqueous solution, wherein the boron exists in a form of boric acid(H₃BO₃) or borate ions (B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻) in the aqueoussolution. The method includes contacting a boron removal medium of theearlier aspect with a first sample of the aqueous solution to removeboron. The method further includes contacting a first boron sensingmedium with the first sample of the aqueous solution after removal ofboron, wherein the first boron sensing medium comprises at least twohydroxyl groups and at least one pyridinic nitrogen, or pyrrolicnitrogen, or quaternary nitrogen. The method also includes obtaining afirst conductivity measurement by measuring conductivity of the firstsample of the aqueous solution after removal of boron and contact withthe first boron sensing medium. The method further includes contacting asecond boron sensing medium with a second sample of the aqueous solutionto form a complex with boron in the second sample, wherein the secondboron sensing medium comprises at least two hydroxyl groups and at leastone pyridinic nitrogen, or pyrrolic nitrogen, or quaternary nitrogen.The method further includes obtaining a second conductivity measurementby measuring conductivity of the second sample of the aqueous solutionafter formation of the complex and correlating the difference in thefirst and second conductivity measurements to the amount of boronpresent in the aqueous solution.

According to yet another aspect of the invention, use of a boron sensingmedium in detecting and quantifying the amount of boron present in anaqueous solution by a conductometric measurement technique is disclosed,wherein the boron exists in a form of boric acid (H₃BO₃) or borate ions(B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻) in the aqueous solution, wherein the boronsensing medium comprises at least two hydroxyl groups and at least onepyridinic nitrogen, or pyrrolic nitrogen, or quaternary nitrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilydrawn to scale, emphasis instead generally being placed uponillustrating the principles of various embodiments. In the followingdescription, various embodiments of the invention are described withreference to the following drawings.

FIG. 1 shows a two-step process to synthesize nitrogen-doped grapheneoxide. Graphite was oxidized into graphene oxide, followed by thenitrogen doping through hydrothermal treatment using ammonia.

FIG. 2(a) shows XPS spectra of GO, and NGO-x; FIG. 2(b) shows atomicratio of N/C, and O/C of the samples calculated from XPS results.

FIG. 3(a) shows the boron absorption capacity of N-GO at varioustemperatures; FIG. 3(b) shows XRD pattern of GO, NGO-60 and NGO-60+B;FIG. 3(c) shows XPS spectra of GO+B, NGO-x+B, and boric acid; FIG. 3(d)shows N-doped atomic ratio of N/C, and the ratios of B/C of the samplescalculated from XPS results; FIG. 3(e) shows high resolution N1s spectraof GO and N-GO-60; FIG. 3(f) shows high resolution B1s spectra of boricacid and N-GO-60+B. Table 1 shows the boron absorption capacity and thecorresponding removal efficiency (%) of N-GO at various temperaturesduring hydrothermal treatment.

FIG. 4(a) shows the kinetics absorption of boron (25 ml boron feedsolution with 20 ppm boron was mixed with 40 mg NGO-60); FIG. 4(b) showsthe effect of pH value of NGO-60.

FIG. 5(a) shows Langmuir isotherms at the temperature 25° C., pH 8.5.Insert: the adsorption performance in DI water synthetic seawater andreal seawater (25 ml boron feed solution with 5 ppm boron was mixed with40 mg N-GO media for 48 hours); FIG. 5(b) shows the regeneration ofN-GO-60 using acid (25 ml boron feed solution with 20 ppm boron wasmixed with 40 mg N-GO media for 48 hours). Table 2 shows parameters ofLangmuir absorption isotherm for N-GO-60 media at 25° C., pH=8.5.

FIG. 6 shows Table 3. Performance comparison of the maximum absorptioncapacity with other media.

FIG. 7(a) shows schematic representation of the boron removal byfiltration process; FIG. 7(b) shows schematic diagrams for removingboron by N-GO.

FIG. 8 shows the ionized complex structure of boric acid and pyridoxinewith (1:1) and (1:2) species ratio.

FIG. 9 shows the boron concentration vs. conductivity with the additionof boric acid into the 16960 ppm of pyridoxine solution in DI water.

FIGS. 10(a) and 10(b) show the Log (Delta Conductivity uS/cm) vs. Log(Boron concentration ppm) in DI water.

FIGS. 11(a) and 11(b) show the Log (Delta Conductivity uS/cm) vs. Log(Boron concentration ppm) in dilute seawater with diluted factor 163times.

FIG. 12 shows the process diagram which can detect the full range ofboron concentration (ppb and ppm).

FIG. 13 shows the simplified process diagram which can detect the ppmlevel of boron concentration.

FIG. 14(a) shows the conductivity contribution from bare vitamin B6 inDI water; and FIG. 14(b) shows the conductivity contribution from boricacid in DI water.

FIG. 15(a) shows the conductivity versus boron concentration in DIwater; and FIG. 15(b) shows the form of log-log from the marked part.Table 4 shows the fitting parameters in FIG. 15(b).

FIGS. 16(a)-(d) show the performance comparisons in diluted seawaterwith a dilution factor of 12 (FIG. 16(a)), 34 (FIG. 16(b)), 124 (FIG.16(c)), and in DI water (FIG. 16(d)); FIG. 16(e) shows the deltaconductivity versus boron concentration; FIG. 16(f) shows the deltaconductivity of FIG. 16(e) in the form of Log (delta conductivity)versus Log (boron concentration).

FIG. 17(a)-(e) show the performance comparisons in diluted seawater witha dilution factor of 34 (FIG. 17(a)), 45 (FIG. 17(b)), 66 (FIG. 17(c)),124 (FIG. 17(d)), and in DI water (FIG. 17(e)); FIG. 17(f) shows thedelta conductivity versus boron concentration; FIG. 17(g) shows thedelta conductivity of FIG. 17(f) in the form of Log (delta conductivity)versus Log (boron concentration).

FIG. 18 shows the performance comparison of vitamin B6 and mannitol inppm range as boron. Table 5 shows the fitting parameters of vitamin B6and mannitol in ppm range as boron.

DESCRIPTION

The following detailed description refers to the accompanying drawingsthat show, by way of illustration, specific details and embodiments inwhich the invention may be practised. These embodiments are described insufficient detail to enable those skilled in the art to practise theinvention. Other embodiments may be utilized and structural, logical,chemical and electrical changes may be made without departing from thescope of the invention. The various embodiments are not necessarilymutually exclusive, as some embodiments can be combined with one or moreother embodiments to form new embodiments.

In aqueous solutions, boron exists in a form of boric acid (H₃BO₃) orborate ions (B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻). According to one aspect of theinvention, there is provided a method of removing or reducing the amountof boron present in an aqueous solution by forming a borate complex. Themethod comprises contacting a boron removal medium with the aqueoussolution to react with the boric or borax species to form the boratecomplex. The method further comprises separating the boron removalmedium from the aqueous solution.

The boron removal medium may comprise a carbon-based material. Thecarbon-based boron removal medium may comprise at least one hydroxylgroup and at least one pyridinic nitrogen, or pyrrolic nitrogen, orgraphitic nitrogen, or amine group. In other words, there is always oneor more hydroxyl groups in the carbon-based boron removal medium.

In various preferred embodiments, the carbon-based material may compriseat least two hydroxyl groups and at least one pyridinic nitrogen, orpyrrolic nitrogen, or graphitic nitrogen, or amine group.

In various alternative preferred embodiments, the carbon-based materialmay comprise at least four hydroxyl groups and at least one pyridinicnitrogen, or pyrrolic nitrogen, or graphitic nitrogen, or amine group.

Preferably, the carbon-based material comprises at least one ofgraphene, graphite, graphene oxide, carbon nanotube, activated carbon,lonsdaleite, fullerene, carbon fibre, carbon black, charcoal, andamorphous carbon.

More preferably, the carbon-based material is doped, such asnitrogen-doped.

In certain preferred embodiments, the carbon-based material may comprisenitrogen-doped (N-doped) graphene oxide or N-doped reduced grapheneoxide. In one exemplified embodiment where N-doped graphene oxide isused as the boron removal medium, the boron absorption capacity can beup to 6.154 mg/g for N-graphene oxide synthesized at 60° C. hydrothermaltreatment.

The hydroxyl group and the pyridinic nitrogen, or pyrrolic nitrogen, orgraphitic nitrogen, or amine group of the carbon-based material may bedirectly covalently bound to the carbon-based material. Alternatively,the hydroxyl group and the pyridinic nitrogen, or pyrrolic nitrogen, orgraphitic nitrogen, or amine group of the carbon-based material may becovalently bound to the carbon-based material via a linker smallmolecule.

In various embodiments, the separating may comprise centrifuging orfiltering the aqueous solution, or the separating may comprise passingwater through the boron removal medium.

According to another aspect of the invention, there is provided a methodof forming the present boron removal medium for use in removing orreducing the amount of boron present in an aqueous solution, wherein theboron exists in a form of boric acid (H₃BO₃) or borate ions (B(OH)₄ ⁻,B₄O₇ ²⁻, H₃BO₂ ⁻) in the aqueous solution.

In various embodiments where the boron removal medium comprises anitrogen-doped graphene oxide, the method comprises oxidizing graphiteto graphene oxide, followed by doping the graphene oxide with ammonia tothereby form the N-doped graphene oxide. By subjecting the grapheneoxide to N-doping, amine groups can be grown on the graphene oxide inorder to enhance the boron absorption ability.

The N-doped graphene oxide may comprise at least one hydroxyl group andat least one pyridinic nitrogen, or pyrrolic nitrogen, or graphiticnitrogen, or amine group. The hydroxyl group may come from the oxidationof the graphite material. Alternatively, the hydroxyl group may comefrom the transformation of a function group, preferably a carboxylgroup, or carbonyl group. In other embodiments, the hydroxyl group maycome from another small molecule comprising a hydroxyl group coupled toa carbon material.

In various embodiments, the nitrogen doping may come from thehydrothermal treatment of carbon materials with ammonia in an autoclave.

In further embodiments, the nitrogen doping may come from ammonia ornitrogen plasma treatment of carbon materials.

In yet further embodiments, the nitrogen doping may come from a directsynthesis of nitrogen doping of carbon materials.

In other embodiments, the nitrogen doping may come from N⁺ion-irradiated carbon materials.

In still further embodiments, the nitrogen doping may come from athermal treatment of carbon materials with ammonia.

Alternatively, the nitrogen doping may come from a chemical treatment ofcarbon materials, preferably hydrazine, or other small molecule withnitrogen or amine group coupled to a carbon material.

Another advantage of the present boron removal medium is the ease ofregenerating a used medium. Accordingly, another aspect of the inventionrelates to a method of regenerating a used boron removal medium. Themethod comprises contacting the used boron removal medium with an acid,followed by rinsing the used boron removal medium with deionized water.

Suitable acids include, but not limited to, sulfuric acid (H₂SO₄) andhydrochloric acid (HCl).

The presently disclosed boron removal medium and method of removing orreducing the amount of boron present in an aqueous solution can beextended to a method of detecting and quantifying the amount of boronpresent in an aqueous solution.

Accordingly, a further aspect of the disclosure relates to a method ofdetecting and quantifying the amount of boron present in an aqueoussolution, wherein the boron exists in a form of boric acid (H₃BO₃) orborate ions (B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻) in the aqueous solution.

The method includes contacting a boron removal medium of the earlieraspect with a first sample of the aqueous solution to remove boron.

The method further includes contacting a first boron sensing medium withthe first sample of the aqueous solution after removal of boron, whereinthe first boron sensing medium comprises at least two hydroxyl groupsand at least one pyridinic nitrogen, or pyrrolic nitrogen, or quaternarynitrogen.

The method also includes obtaining a first conductivity measurement bymeasuring conductivity of the first sample of the aqueous solution afterremoval of boron and contact with the first boron sensing medium.

The method further includes contacting a second boron sensing mediumwith a second sample of the aqueous solution to form a complex withboron in the second sample, wherein the second boron sensing mediumcomprises at least two hydroxyl groups and at least one pyridinicnitrogen, or pyrrolic nitrogen, or quaternary nitrogen.

The method further includes obtaining a second conductivity measurementby measuring conductivity of the second sample of the aqueous solutionafter formation of the complex and correlating the difference in thefirst and second conductivity measurements to the amount of boronpresent in the aqueous solution.

In various embodiments, each of the first and second boron sensing mediacomprises at least two hydroxyl groups and at least one pyrrolicnitrogen. For example, the first and/or second boron sensing medium maycomprise three hydroxyl groups and one pyrrolic nitrogen. One disclosedembodiment of the first and/or second boron sensing medium is pyridoxine(i.e. vitamin B6) illustrated in FIG. 8.

Alternatively, each of the first and second boron sensing media maycomprise at least four hydroxyl groups and at least two pyrrolicnitrogen.

In yet further embodiments, each of the first and second boron sensingmedia comprises pyridoxine or a derivative thereof.

Advantageously, the method disclosed herein enable the detection andquantification of the amount of boron in the ppm, ppb, and even pptlevels.

According to yet another aspect of the invention, use of a boron sensingmedium in detecting and quantifying the amount of boron present in anaqueous solution by a conductometric measurement technique is disclosed,wherein the boron exists in a form of boric acid (H₃BO₃) or borate ions(B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻) in the aqueous solution, wherein the boronsensing medium comprises at least two hydroxyl groups and at least onepyridinic nitrogen, or pyrrolic nitrogen, or quaternary nitrogen.

In order that the invention may be readily understood and put intopractical effect, particular embodiments will now be described by way ofthe following non-limiting examples.

EXAMPLES Example 1. Nitrogen-Doped Graphene Oxide Toward EffectiveRemoving Boron Ions From Sea Water

In this example, it is demonstrated the synthesis of a novel boronremoval medium, namely nitrogen-doped graphene oxide (N-GO), via asimple two-step process: (1) oxidation of carbon material to form the—OH group, (2) nitrogen-doped by hydrothermal method to incorporatenitrogen into graphene oxide in order to enhance the boron adsorptionability. Significantly, the N-GO can be directly used in seawaterwithout any treatment, which is not common for most of the other currenttechnologies. N-GO exhibits the adsorption capacity of 6.55 mg/g mediaat 25 ml of feed with 20 ppm boron for 40 mg media, and thecorresponding rejection is 52.40%. In 5 ppm boron feed, this media canachieve a boron rejection up to 91.12%. In real seawater with 5 ppm ofboron, N-GO also shows an up to 2.42 mg/g capacity, which corresponds to77.44% rejection. The maximum adsorption capacity is 58.7 mg/g based onLangmuir adsorption isotherm, the highest among all the sorbentsproducts at present. The high adsorption capability of N-GO was shown tobe attributed to the high amount of hydroxyl group and the surface areaof graphene oxide, as well as the enhanced adsorption fromnitrogen-doped effect. The influences from pH, other ions, kineticsadsorption were investigated. It was found that the N-GO media isextremely effective in a wide range of pH conditions as well as in realconditions of seawater. Moreover, this boron removal media can be easilyregenerated for further use with a simple acid treatment. Therefore, thepromising result reported herein has a strong potential to greatlyimpact the field of boron removal, particularly in the water industry.

Materials.

Graphite powder, aqueous ammonia (28 wt %), 30 wt % H₂O₂, NaNO₃, K₂S₂O₈,P₂O₅ and KMnO₄ were purchased from Sigma-Aldrich. 65 wt % HNO₃ and 98 wt% H₂SO₄ were bought from Merck. All the reagents were used as receivedwithout further purification.

Preparing Graphene Oxide.

Preparation of graphene oxide (GO): Graphene oxide (GO) was synthesizedusing natural graphite powders by a modified Hummers method. Briefly, 2g of graphite powder was added into a mixture of 12 ml of 98% H₂SO₄, 2.5g K₂S₂O₈, and 2.5 g of P₂O₅. The solution was kept at 80° C. for 4.5 hfollowed by thorough washing with water (through filtration) and ovendrying at 60° C. Subsequently, the as-treated graphite was put into abeaker, and 100 ml of H₂SO₄ were added while keeping the beaker in anice bath. Afterwards, 13 g of KMnO₄ was then added slowly. After 5 min,the ice bath was removed, and the solution was heated up and kept at 35°C. under vigorous stirring for 4 h, followed by the slow addition of 200ml of water. Finally, 16 ml H₂O₂ was added, followed by centrifugationand washing with 1 litre dilute HCl (1 HCl: 10 DI water). Theexfoliation of GO was achieved by sonication.

Preparing N-Doped Graphene Oxide as Boron Removal Media.

Some amounts of aqueous ammonia (8 ml, 28 wt %) was added into the abovedispersion of GO (37.5 ml, 4 mg/ml) under magnetic stirring. Then themixture was transferred into Teflon-lined autoclave at room temperatureand heated at 40° C.-140° C. for 5 h without stirring before naturalcooling. The products of nitrogen-doped graphene oxide were rinsed withDI water to remove the excessive or physisorbed ammonia, and the powderform of products were collected as boron removal media.

Boron Removal and Measurement.

In the batch system, 25 ml boron feed solution with 20 ppm boron wasmixed with 40 mg N-doped graphene oxide, kept stirring for 48 h,followed by centrifuge or filtration with 220 nm nylon filter paper, thefiltered solution was collected for boron analysis. The followingequation was used to calculate boron adsorption capacity at equilibrium:

$\begin{matrix}{Q_{e} = {\left( {C_{0} - C_{e}} \right)\frac{V}{M}}} & (1)\end{matrix}$

where C_(o) (mg/l) and C_(e) (mg/l) are defined as the initial and finalconcentrations of boron respectively, V (l) is considered as the volumeof the solution and M (g) is the mass of N-GO media. Boron rejection canbe calculated based on the equation: Boron Rejection(%)=(1−C_(e)/C_(o))*100%. ICPE-9820 plasma atomic emission spectrometerwas used to analysis the boron concentration. X-ray photoelectronspectroscopy (XPS) analyses were conducted by PHI Quantera II with amonochromatic Al Kα X-ray source (1486 eV) to investigate the surfacechemistries of the obtained samples.

Regeneration Process of Boron Removal Media.

For a typical regeneration process, 3-5 bed volume (BV) of an aqueoussolution of 5% HCl or H₂SO₄ is applied and the regenerate contact timewas kept for 60 min. Thereafter, the medium is rinsed with 8-10 BV of DIwater. At the conversion step, 3-5 BV of 2.5% NaOH was used, andfollowed by the DI water rinse.

Results and Discussions

N-GO Synthesis Process and Analysis.

FIG. 1 describes the synthesis of N-GO in two simple steps. During thefirst step, graphite is oxidized and exfoliated into graphene oxide (GO)by a modified Hummer's method. Following that, a hydrothermal stepinvolving GO and aqueous ammonia are applied to obtain N-GO. After thehydrothermal treatment, the color of N-GO solutions changed from brownto dark brown, suggesting a partial removal of oxygen-containingfunctional groups. XPS spectra of GO, and NGO-x were shown in FIG. 2(a).The samples are denoted as N-GO-x, where x represents the reactiontemperature (in ° C.) during hydrothermal treatment. An increase in theintensities of N1s peak at ˜400 eV with increasing reaction temperaturesindicates that nitrogen doping has occurred for the GO. The doping of GOoccurs via the formation of covalently bonded nitrogen and simultaneousde-oxygenation of several oxygenated functional groups on the surface ofGO, and the atomic ratio of N/C and O/C was shown in FIG. 2(b) based onthe XPS results. The extent of nitrogen doping is directly proportionalto the reaction time and hydrothermal temperature where longer reactiontimes and higher temperatures produce a greater amount of nitrogen dopedsites.

Boron Absorption Properties of N-GO-x and Characterization.

In a typical boron removal experiment, 25 ml of boron feed solution at aconcentration of 20 ppm boron is mixed with 40 mg of N-doped GO andstirred for 48 h followed by centrifugation or filtration in a batchstudy. The filtered solution is collected for boron analysis and theadsorption capacity is calculated. FIG. 3(a) shows the boron adsorptioncapacity of GO and N-GO-x (where x=RT, 40, 60, 80, 100 and 140° C.). Theoptimal hydrothermal temperature is around 60° C., where the boronadsorption capacity is up to 6.55 mg/g N-GO. A summary of the presentexperiments is shown in Table 1. At an increased temperature above 80°C., the boron adsorption capacity decreases exponentially withincreasing reaction temperatures. This can be attributed to asignificant reduction of —OH functional groups. As a result, the boroncomplexes are unable to form. Ammonia concentration used during thehydrothermal step is another factor which can affect the adsorptioncapacity. The optimal ammonia concentration is found to be between 2%and 3% for 150 mg GO (not shown). At low ammonia levels, there isnegligible nitrogen doping which results in the low boron adsorptioncapacities. At high ammonia concentrations, the increase in nitrogendoping and the reduction effect from the excess ammonia may result inthe excessive loss of hydroxyl group in GO (not shown).

The effect of de-oxygenation and boron-adsorption were analyzed usingX-ray diffraction, as shown in FIG. 3(b). The diffraction peak of GO islocated at 9.22°, which corresponds to an interlayer distance of 1.09nm. The hydrothermal treatment with ammonia at 60° C. reduces theinterlayer distance to 0.91 nm due to the de-oxygenation effect.However, the interlayer distance increases to 0.98 nm when the boronspecies were absorbed on the surface of NGO-60.

X-ray photon spectroscopy (XPS) was used to characterize the extent ofnitrogen doping and the amount of boron adsorbed by quantitativelyanalyzing the element composition of the samples from peak area (C1s, N1s and B1s). FIG. 3(c) shows XPS profiles of NGO-x after boronabsorption. An appearance in the peak of the B1 s at ˜192 eV indicatesthat boron absorption has occurred for the NGO. The nitrogen-dopingcauses N-GO to have an overall positive charge with respect to undopedGO. The increased surface charge induces an electrostatic attractionbetween the nitrogen-doped sites on the GO surface and the negativelycharged B(OH)₄ ⁻ species. As the B(OH)₄ ⁻ species is brought close tothe N-GO surface, hydrogen-bonding donoracceptor interactions occurbetween the OH from the boric acid/borate ion and the —OH/—NH— from N-GOand this results in the formation of a stable boron complex.

FIG. 3(d) further shows that the nitrogen content (N/C) of the sampleshas increased from 0.06 to 0.08 as reaction temperatures increased from60 to 140° C. (not shown). This implies that there is an increasingamount of nitrogen content in the GO with increasing hydrothermaltemperature. On the other hand, it can be observed that the B/C contentis inversely proportional to the reaction temperature where the highestB/C ratio is 0.19 for NGO-60 sample. Hence, this suggests that 60° C. isthe optimal temperature for the synthesis of N-GO with the highest boronadsorption capacity (FIG. 3(a)). This can be explained by consideringthe unique roles of both nitrogen and —OH functional groups where theformer facilitates the localized positive attraction of boric acid to GOsurfaces and the latter allows the formation of stable complex betweenboric acid and N-GO. However, as nitrogen doped results in thesimultaneous deoxygenation of GO, an optimal condition is necessary. Thehigh-resolution XPS N1s spectrum is illustrated in FIG. 3(e) for the GOand optimal sample N-GO-60. The main peak of N1s spectrum present at397.75 eV corresponds to the pyridinic N while weaker peak comes frompyrrolic N (399.75 eV), and the minor peak is assigned to graphitic N(402 eV).

The high resolution XPS of B1 s is shown in FIG. 3(f). The B₁ s peaksignificantly blue-shifts to higher binding energy after a boron complexhave formed. This might be due to a reduction effect from the N-GO. Inthe B1 s peak for the N-GO-60+B, there are two peaks overlap together.The peak 191.75 eV can be likely attributed to the edge effects of thesample and the other minor peak can be assigned to the configurationshown at the center.

The Boron Kinetics Absorption of N-GO-60 and the Effect of pH Value.

In order to explore the kinetics adsorption of boron, the batchexperiments were conducted at room temperature using 5 ppm, 20 ppm, and100 ppm boron feed. The pH value was kept constant at the original valueof the solutions (˜8.5). The results obtained are shown in FIG. 4(a). Ingeneral, the boron adsorption capacity increases with an increasingcontact time until adsorption saturation. Based on the curve, anequilibrium is reached after twenty hours for these three solutions. Thesaturated adsorption capacity is 6.55 mg/g for solution with initialconcentration of 20 ppm, which corresponds to 52.40% boron rejection.However, the feed concentration of 5 ppm delivers the highest efficientboron rejection, which can be up to 91.12%. When the amount of N-GO isincreased to 110 mg from 40 mg using 25 ml, 5 ppm feed, 0.0630 ppm boronproduct can be obtained in the product solution prepared with deionizedwater, and the boron rejection rate is calculated to be up to 98.74%.

As shown in previous reports, the pH value plays an important role inthe boron adsorption process. Therefore, it was investigated the pHeffect and the results are shown in FIG. 4(b). The experiments werecarried out with initial concentration of 20 ppm B with 25 ml feed. 40mg of N-GO-60 media was added in the batch testing. The pH value wasadjusted with HCl or NaOH. The mixture was stirred for 48 hours followedby centrifuge or filtration with 220 nm nylon filter paper, the filteredsolution was collected for boron analysis. As displayed in FIG. 4(b),N-GO-60 shows a high selectivity for the boron at pH 8.6. The lowestadsorption capacity was achieved at pH 2.0. The pH value in the solutioncontrols the distribution of boric acid molecular and borate ion, whichcan affect the efficiency of boron removal. At low pH levels, boric acidpredominates in the aqueous solution. This uncharged species willsuppress the complex formation and result in low boron removalefficiency. At high pH (>9) levels, borate ion is the primary species insolution. However, as the boron complex at basic pH is carried out byhydroxyl groups on GO surfaces, this implies that the surface of N-GO-60is more negatively charged in the basic media due to high OH ionspresent in the solution, which results in low boron loading. Thefavorable pH range is shown to be between 6 and 10. Despite this, theinfluence of pH in the media only resulted in a small fluctuation ofboron adsorption capacity (maximum 20% over pH 2-13 range). It is notedthat sea water has a pH value (8.4), which is within the highestadsorption range for the present materials. This indicates that theN-GO-60 can be highly useful for sea water boron ion removal.

Boron Adsorption Equilibrium Isotherm, the Adsorption Performance inReal Seawater, and the Regeneration of N-GO-60.

Langmuir isotherm model was chosen to analyze boron adsorptionequilibrium isotherm based the adsorption data. The equation of Langmuiradsorption isotherm is presented as follows,

$\begin{matrix}{q_{e} = \frac{Q_{m}K_{L}C_{e}}{1 + {K_{L}C_{e}}}} & (2)\end{matrix}$

where C_(e) is the equilibrium concentration of the adsorbate and q_(e)is the adsorption capacity adsorbed at equilibrium, Q_(m) is maximumadsorption capacity and K_(L) is the Langmuir adsorption constant. Asshown in FIG. 5(a), Q_(m) can be estimated as 58.70 mg/g, and K_(L) is0.00409 l/mg. The parameters of Langmuir adsorption isotherm arepresented in the Table 2. It was found that the Langmuir isotherm modelrepresented the measured sorption data well based on the correlationcoefficient of R²=0.985. The performance comparison of the maximumadsorption capacity was conducted in the Table 3, FIG. 6. With anextremely high maximum adsorption capacity of 58.7 mg/g, this makes theN-GO the best reported sorbents to-date. The good correlationcoefficient values imply a strictly localized monolayer sorptionphenomenon occurring in the media. In the Langmuir sorption isothermmodel, it is assumed that the sample surface is homogeneous, where thesurface containing the adsorbing sites is perfectly flat plane with nocorrugations. The huge amount of the surface area of graphene oxide withhomogenous sorption patches and active sites from hydroxyl group ofgraphene oxide may lead to high adsorption capacity.

In order to evaluate the interference from other ions or molecules, acomparison study is conducted as shown in the insertion of FIG. 5(a). Ina feed solution prepared with deionized water, the adsorption capacityis 2.84 mg/g N-GO-60. The real seawater with 2.67 ppm boron wascollected from the ocean of East Coast Park, Singapore. Pre-filtrationwas conducted to remove the particles. Additional boric acid was addedto reach the average 5 ppm boron as feed. The adsorption capacity dropsa little to 2.42 mg/g N-GO, which suggests that as high as 85%adsorption capacity can be maintained even in real seawater. Thisimplies that the nitrogen doped graphene oxide is unreactive to otherions or molecules and is highly selective towards boron.

As shown in FIG. 5(b), this boron removal media can be regenerated withacid, which means that the trapped boron can be removed from theexhausted N-GO through the addition of an acid solution (HCl or H₂SO₄)into the media. Strong acids were required to break down the formedassociation of borate-NGO complex, where boron was released to elute. 5%HCl was chosen for regeneration. 3-5 bed volume (BV) HCl of an aqueoussolution is very effective with a 1 hour contact time for the removal ofboron from N-GO. After that, 3-5 BV of 2% NaOH rinse was used asneutralization step to neutralize the added acid, followed by the 8-10BV DI water rinse. After regeneration, the N-GO media may be reused forthe next loading cycle. The regenerated result is shown in FIG. 5(b),four cycles were carried out during the test. After regeneration, thecapacity still can be maintained at ˜86% and ˜81% for the 2^(nd) and3^(rd) cycles. Based on the image of inserted SEM in FIG. 5(b), afterfour cycles, the morphology of NGO keep the same, which indicates thatit can be continued to recycle.

Boron Removal Mechanism.

Boron atoms exist in the form of negatively charged B(OH)₄ ⁻ ion andboric acid. It is known that some compounds with adjacent hydroxylgroups have a good affinity to boron acid or borate ions. The possiblereaction mechanism for the removal of boron appears to be the formationof complexes, and a schematic diagram of the reaction pathway is shownin FIGS. 7(a) and 7(b). The removal of boron ions occurs in two steps,physisorption of boron ions and chemical bonding of boron ions tospecific sites. Since GO is intrinsically negatively charged, boron ionsare electrostatically repelled from the surface of GO and that resultsin a low adsorption capacity. Nitrogen doped of GO has two advantageouseffects: (1) increased electrostatic attraction of B(OH)₄ ⁻ ions to N-GOsurface and (2) enhancement in binding sites. Firstly, the presence ofnitrogen atoms induces a positive charge density in the carbon atomsadjacent to them and this will result in an enhanced adsorption of boronions to the surface of N-GO. Secondly, —OH groups attached to carbonatoms adjacent to nitrogen doped sites experience increased affinity toboron ions and are able to form complexes more effectively. In order toshow the function of N doping for GO modification, it is also measuredthe zeta potential for both GO and N-GO (not shown) and the result showsan improvement in surface charge for N-GO over GO. The overall zetapotential for N-GO is still negative because induced positive chargesare only localized at nitrogen doping sites. The enhancement in bindingsites is further verified through Density Functional Theory (DFT)calculations. The bonding energies for N-GO and GO are calculated (notshown) as −2.67 eV and −1.87 eV, respectively, which indicates higherpossibility to promote the chemical reaction reacted for the N-GO.

Example 2. Full Range Boron Measurement in Aqueous Solutions

In this example, a simple and efficient method and apparatus todetermine boron concentration using conductometric measurementtechniques in the aqueous solution based on the chemical reactionbetween boric acid and novel reagent, pyridoxine are disclosed. Thepyridinic-N in pyridoxine can enhance the highly ionized complexformation between boric acid and pyridoxine. The boron concentration insample is proportional to the conductivity difference caused by theionized complex formation of boric acid and pyridoxine. The processdiagram is designed to detect the full range of boron concentration(ppb, ppm level) based on the background measurement ofpyridoxine/boron-free water, as well as a simplified one which issuitable for ppm level monitor with direct pyridoxine dosage.

With reference to FIG. 8, it shows a possible reaction between boricacid and pyridoxine. This has been proven that pyridoxine has a goodaffinity to boron in aqueous solutions. It is known that some compoundswith adjacent hydroxyl groups show an appreciable tendency to formcomplexes with boric acid and borate ions. The predominant mechanismappears to be the formation of pyridoxine-boron complexes. The complexescontaining one pyridoxine per boric acid could be formed with thefollowing (1:1) structure shown in FIG. 8, and (1:2) stable speciesratio when two molecules of pyridoxine is involved.

FIG. 9 shows the boron concentration versus conductivity with theaddition of boric acid into the 16960 ppm of pyridoxine solution in DIwater. The measured boron concentration is from 0 ppm to 525 ppm. Thisresponse is slightly curved due to the chemometric analysis of thereactions in terms of conductivity. The conductivity of the samplestream is measured before and after injection of boric acid intosolution. With the increased boric acid amount, the conductivity keepgoing up, which indicates that the highly ionized complex formationbetween boric acid and pyridoxine in the sample. The conductometricmeasurement can be detected due to the highly ionized nature of thereaction. When the free pyridoxine is consumed completely in solution,the conductivity will maintain or decrease a little with the increasedboric acid concentration. The estimation shows the complexes betweenboric acid and pyridoxine could be formed with the (1:2) stable speciesmolar ratio structure.

The log-log plot of the same data shown in FIG. 9 is presented in FIG.10. The Y-axis shows the Log (delta conductivity) after pyridoxineconductivity is subtracted from the conductivity ofpyridoxine/boron-containing samples. The linear part is taken andplotted in FIG. 10(b) with the slope 0.9261, the intercept −0.1836, andthe R2 value of 0.9984, which illustrates that Log (delta conductivity)can be proportional to the log (boron ppm) mathematically. Thus theunknown boron concentration can be determined by the conductivitymeasurement.

FIGS. 11(a) and 11(b) show the linear behavior of Log (DeltaConductivity uS/cm) vs. Log (Boron concentration ppm) in dilute seawaterwith diluted factor 163 times. The R2 value is 0.9987, which illustratesthat Log (delta conductivity) can be proportional to the log (boron ppm)mathematically. The linear behavior means that the reagent pyridoxinecan only complex with boron, others even in seawater do not affect theboron measurement.

To compare the ionized complex effect from pyridoxine, the conductivityfrom bare boric acid was measured. The results show that theconductivity will change from 1 to 8 uS/cm with the boron concentration0-2000 ppm. This will not affect the ppm level boron measurement.However, regarding to the low boron concentration measurement, ultrapurewater and pyridoxine are required. Additional process is needed toremove ions and boron in order to detect the ppb or even ppt levelboron. The design diagram is shown in FIG. 12. Pyridoxine reagent iscontinuously recirculated through the reagent column to remove the ionsand further purify pyridoxine. During the zero measurement to be made,ion and boron are removed before injection valve. Purified pyridoxine isdosed into the stream and causes a conductivity peak which is measuredby the conductivity cell. During a sample measurement, the samplesolution is sent directly to the injection valve. Sample conductivity ismeasured. When the reagent pyridoxine is injected, a higher conductivitypeak can be observed due to the highly ionized complex formation betweenboron and pyridoxine. The concentration of boron in sample isproportional to the conductivity difference between the zero and sampleconductivity peaks. Therefore, a highly accurate concentrationmeasurement can be obtained. Due to the highly ionized property of thecomplex, very low levels of boron are detectable. This is suitable forthe ppb even ppt, and ppm level boron measurement depending on thedetected range of the conductivity cell.

In order to measure directly ppm level boron, a simplified fluidic blockdiagram is shown in FIG. 13. The pyridoxine reagent is directly dosedinto the zero stream and sample stream. The detected range ofconductivity cell is in uS/cm.

In summary, a full range boron sensor is demonstrated based on the novelreagent, pyridoxine, which can react with boric acid to form an ionizedcomplex. The boron concentration in sample is proportional to theconductivity difference caused by the ionized complex formation of boricacid and pyridoxine. The process diagram is designed to detect the fullrange of boron concentration (ppb, ppm level), as well as a simplifiedone which is suitable for ppm level monitor with direct pyridoxinedosage. This is the simple and effective technology for the boronmeasurement. This invention will be direct application in boronmeasurement field.

Example 3. Determination of Boron Concentration in Aqueous SolutionsBased on Ionic Complex Formation

In this example, a simple and effective method is proposed to determinethe boron concentration by using electrical conductivity measurementtechniques in the aqueous solution based on the ionized complex formedbetween boron species and vitamin B6. The conductivity of the ionizedcomplex can be easily detected and accurately measured using aconductivity meter. The boron concentration in the sample is correlatedto the conductivity caused by the ionized complex formation. This workprovides a cost-effective technology for the boron measurement invarious solutions, which will be of great industrial importance in boronmeasurement field.

Materials and Experimental Process.

Boric acid and vitamin B6 (≥98%) was purchased from Sigma-Aldrich. Thesechemicals were used as received without further purification. Seawaterwas collected from the ocean of East Coast Park, Singapore. Vitamin B6was dissolved in DI water, or diluted seawater. The solution wasaliquoted to several 50 ml beakers. The conductivity was measured withDDSJ-308F conductivity meter, and the reading was obtained afterstirring and stability with the addition of boric acid. The actual boronconcentration was analyzed by ICPE-9820 plasma atomic emissionspectrometer.

Results and Discussion

Both vitamin B6 and boric acid are non-conductive by themselves in theaqueous solutions. The conductivity from bare vitamin B6 or bare boricacid was measured, as shown in FIGS. 14(a) and 14(b). The conductivitykeeps going up with increased concentration. For vitamin B6, it ismainly due to the <2% impurity. It is possible that vitamin B6 itselfionizes to a small extent. Regarding the boric acid, about 3 uS/cmconductivity increment was contributed by 950 ppm boron, which isnegligible. This will not affect boron measurement in the ppm range.

Boron is present in aqueous water as boric acid and borate ion. It isweakly ionized acid product in water, the pKa of H₃BO₃/B(OH)₄ ⁻ is 9.2at 25° C. Therefore, boric acid will dominate at normal drinking water,seawater, or DI water. The relation of the two species can be given bythe following equation, as shown in Equation (3). It is known that somecompounds with adjacent hydroxyl groups show an appreciable tendency toform complexes with boric acid and borate ions. It has been proven thatboric species can easily react with vitamin B6, and the reaction isshown in Equation (4). Vitamin B6 has a good affinity to boron inaqueous solutions, and can form a highly ionized boron-vitamin B6complex, which can cause a dramatic increase in electrical conductivity.With the consuming of borate ion during the complex formation, theequilibrium in Equation (3) is typically towards the right until theexhaust of vitamin B6.

The measuring correlation between boron concentration and conductivityis presented in FIGS. 15(a) and 15(b). The vertical axis shows theconductivity signal. The conductivity was obtained after stability ofconductivity reading with the addition of boric acid. With the increasedboric acid concentration, the conductivity keeps going up, whichindicates the formation of highly ionized complex between boric acid andvitamin B6. When free vitamin B₆ is completely exhausted in solution,the conductivity will maintain or even slightly decrease with theincreased boric acid, as shown in saturated conductivity part in FIG.15(a). Within the area marked inside the dotted box, conductivity isproportional to the boron concentration. The measured boronconcentration is from 0 ppm to 550 ppm. The lightly curved trend ofconductivity is due to the chemometric analysis of the reactions. Thedramatic change part of conductivity marked in the red area wasre-plotted in the form of log-log as shown in FIG. 15(b). The Y-axisshows the log (delta conductivity) after vitamin B6 conductivity issubtracted from that of vitamin B6/boron-containing samples. The log(delta conductivity) is linearly correlated to the log (boronconcentration) with the slope 0.89782, the intercept −0.14152. It wasfound that the measured data can fit well with the correlationcoefficient (R²) of 0.99882, which means boron concentration can beaccurately determined mathematically by the conductivity signal. Theobtained parameters of fitting are presented in the Table 4. In thecurrent condition, the boron concentration can be empirically derived asbelow Equation (5). Thus the unknown boron content in aqueous sample canbe quantified by the conductivity measurement.

Boron Concentration=1.4376*(Delta Conductivity)^(1.1138)  (5)

Herein it was noted that the purity of vitamin B6 is the key factor toinfluence the lower limit of detection. In the current test condition,there is still around 2% impurity in the reagent, which will affect themeasurement of lower concentration. The procedure of pre-purificationand deionization is required to remove these interfering ions for thesuper low boron determination. This step is of critical importance foraccurate detection of ppb or ppt level. Another issue is that resolutionof the conductivity meter. The meter of super low detection range andresolution is also necessary for low limit of detection. For example,nS/cm for ppb, even ppt level of boron detection, uS/cm for ppm level ofboron detection.

In order to explore the application scope of this sensor, the dilutedseawater was used as feed sample. The diluted factor was controlled at12, 34, and 124 times, as shown in FIG. 16(a)-(f). Seawater wascollected from the ocean of East Coast of Singapore, and thepre-filtration was carried out to remove the small particles. With theincreased salt concentration, the delta conductivity becomes smaller andsmaller, especially at the high boron concentration area. At the dilutedfactor of 12, the linear behavior of log-log is no longer valid, whichmeans the measurement is not accurate. It is due to the serousinterference caused by some ions or compounds in seawater. Therefore,this would be the upper limit in the current test. In order to test thishypothesis, several lower concentrations of diluted seawater sampleswere carried out with the diluted factor 124, 66, 45, 34, as presentedin FIG. 17(a)-(g), the entire curves show the linear behavior. Thisdemonstrates that the sensor can work well even at the diluted seawaterwithin the 0-1,600 uS/cm range. Other ions or compounds in seawater donot affect the boron measurement.

Mannitol is currently the most commonly used chemical reagent for borondetermination. Herein, the performance comparison was conducted betweenmannitol and vitamin B6 prepared in DI water within the ppm range. Asshown in FIG. 18 and the fitting parameters in Table 5, the R² is higherfor vitamin B6 than that of mannitol, which means that it is moreaccurate for vitamin B6. The sensitivity is the other critical factor.The fitting value of slope shows a double improvement for the vitaminB6, compared with mannitol, which give the proof that vitamin B6 is muchsuperior to mannitol in ppm range. It may be due to the enhanced ionizednature of complex between boric acid and vitamin B6 from thepyridinic-N.

Accordingly, vitamin B6 has been demonstrated as a novel reagent for aquick, accurate, economic, portable, and highly sensitive boron detectorbased on the conductance measurement techniques. It can react with boricacid to form an ionized complex resulting in a measurable increase ofconductivity in aqueous solution. The true boron concentration inboron-containing sample has been found to be mathematically correlatedto electrical conductivity difference. This sensor can be applicable inDI water or even diluted seawater within 0-1,600 uS/cm of feed samples,and there is trivial influence of interference observed. Some other ionsor compounds in diluted seawater could interfere with the determinationof boron, especially at the high salt concentration. Based on theperformance comparison between vitamin B6 and mannitol, it can beconcluded that both accurateness and sensitivity of vitamin B₆ are muchsuperior in ppm range, compared with that of mannitol due to theenhanced ionized complex formation from the pyridinic-N in vitamin B6.This is a simple and effective technology for highly accurate boronmeasurement in the aqueous solution, and suitable for online analyzer.This invention will have direct applications in boron measurement field.

By “comprising” it is meant including, but not limited to, whateverfollows the word “comprising”. Thus, use of the term “comprising”indicates that the listed elements are required or mandatory, but thatother elements are optional and may or may not be present.

By “consisting of” is meant including, and limited to, whatever followsthe phrase “consisting of”. Thus, the phrase “consisting of” indicatesthat the listed elements are required or mandatory, and that no otherelements may be present.

The inventions illustratively described herein may suitably be practicedin the absence of any element or elements, limitation or limitations,not specifically disclosed herein. Thus, for example, the terms“comprising”, “including”, “containing”, etc. shall be read expansivelyand without limitation. Additionally, the terms and expressions employedherein have been used as terms of description and not of limitation, andthere is no intention in the use of such terms and expressions ofexcluding any equivalents of the features shown and described orportions thereof, but it is recognized that various modifications arepossible within the scope of the invention claimed. Thus, it should beunderstood that although the present invention has been specificallydisclosed by preferred embodiments and optional features, modificationand variation of the inventions embodied therein herein disclosed may beresorted to by those skilled in the art, and that such modifications andvariations are considered to be within the scope of this invention.

By “about” in relation to a given numerical value, such as fortemperature and period of time, it is meant to include numerical valueswithin 10% of the specified value.

The invention has been described broadly and generically herein. Each ofthe narrower species and sub-generic groupings falling within thegeneric disclosure also form part of the invention. This includes thegeneric description of the invention with a proviso or negativelimitation removing any subject matter from the genus, regardless ofwhether or not the excised material is specifically recited herein.

Other embodiments are within the following claims and non-limitingexamples.

In addition, where features or aspects of the invention are described interms of Markush groups, those skilled in the art will recognize thatthe invention is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

1. A method of removing or reducing the amount of boron present in anaqueous solution, wherein the boron exists in a form of boric acid(H₃BO₃) or borate ions (B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻) in the aqueoussolution, the method comprising: contacting a boron removal medium withthe aqueous solution, wherein the boron removal medium comprises acarbon-based material comprising at least one hydroxyl group and atleast one nitrogenous group selected from the group consisting of apyridinic nitrogen, a pyrrolic nitrogen, a graphitic nitrogen, an aminegroup, and combinations thereof; wherein the carbon-based materialcomprises at least one of a graphene, a graphite, a graphene oxide, acarbon nanotube, an activated carbon, lonsdaleite, a fullerene, a carbonfiber, a carbon black, a charcoal, and an amorphous carbon; andseparating the boron removal medium from the aqueous solution. 2-6.(canceled)
 7. The method according to claim 1, wherein the carbon-basedmaterial comprises nitrogen-doped graphene oxide.
 8. (canceled)
 9. Themethod according to claim 1, wherein the at least one hydroxyl group andthe at least one nitrogenous group are directly covalently bound to thecarbon-based material.
 10. The method according to claim 1, wherein theat least one hydroxyl group and at least one nitrogenous group arecovalently bound to the carbon-based material via a linker smallmolecule.
 11. The method according to claim 1, wherein either the atleast one hydroxyl group or the at least one nitrogenous group arecovalently bound to the carbon-based material via a linker smallmolecule.
 12. The method according to claim 1, wherein the separatingcomprises centrifuging or filtering the aqueous solution, or theseparating comprises passing water through the boron removal medium. 13.A boron removal medium for use in removing or reducing the amount ofboron present in an aqueous solution, wherein the boron exists in a formof boric acid (H₃BO₃) or borate ions (B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻) in theaqueous solution, wherein the boron removal medium comprises acarbon-based material comprising at least one hydroxyl group and atleast one nitrogenous group selected from the group consisting of apyridinic nitrogen, a pyrrolic nitrogen, a graphitic nitrogen, an aminegroup, and combinations thereof; wherein the carbon-based materialcomprises at least one of a graphene, a graphite, a graphene oxide, acarbon nanotube, an activated carbon, a lonsdaleite, a fullerene, acarbon fiber, a carbon black, a charcoal, an amorphous carbon, andcombinations thereof. 14-17. (canceled)
 18. The boron removal mediumaccording to claim 13, wherein the carbon-based material isnitrogen-doped.
 19. The boron removal medium according to claim 18,wherein the carbon-based material comprises nitrogen-doped grapheneoxide.
 20. (canceled)
 21. The boron removal medium according to claim13, wherein the at least one hydroxyl group and the at least onenitrogenous group of the carbon-based material are directly covalentlybound to the carbon-based material.
 22. The boron removal mediumaccording to claim 13, wherein the at least one hydroxyl group and theat least one nitrogenous group of the carbon-based material arecovalently bound to the carbon-based material via a linker smallmolecule.
 23. The boron removal medium according to claim 13, whereineither the at least one hydroxyl group or the at least one nitrogenousgroup of the carbon-based material is covalently bound to thecarbon-based material via a linker small molecule. 24-36. (canceled) 37.A method of detecting and quantifying the amount of boron present in anaqueous solution, wherein the boron exists in a form of boric acid(H₃BO₃) or borate ions (B(OH)₄ ⁻, B₄O₇ ²⁻, H₃BO₂ ⁻) in the aqueoussolution, the method comprising: contacting a boron removal medium witha first sample of the aqueous solution to remove boron, wherein theboron removal medium comprises a carbon-based material comprising atleast one hydroxyl group and at least one nitrogenous compoundcomprising at least one of a pyridinic nitrogen, a pyrrolic nitrogen, agraphitic nitrogen, an amine group, and combinations thereof; whereinthe carbon-based material comprises at least one of a graphene, agraphite, a praphene oxide, a carbon nanotube, an activated carbon, alonsdaleite, a fullerene, a carbon fiber, a carbon black, a charcoal, anamorphous carbon, and combinations thereof; contacting a first boronsensing medium with the first sample of the aqueous solution afterremoval of boron, wherein the first boron sensing medium comprises atleast two hydroxyl groups and at least one nitrogenous group selectedfrom the group consisting of a pyridinic nitrogen, a pyrrolic nitrogen,a quaternary nitrogen, and combinations thereof; obtaining a firstconductivity measurement by measuring conductivity of the first sampleof the aqueous solution after removal of boron and contact with thefirst boron sensing medium; contacting a second boron sensing mediumwith a second sample of the aqueous solution to form a complex withboron in the second sample, wherein the second boron sensing mediumcomprises at least two hydroxyl groups and at least one pyridinicnitrogen, or pyrrolic nitrogen, or quaternary nitrogen; obtaining asecond conductivity measurement by measuring conductivity of the secondsample of the aqueous solution after formation of the complex; andcorrelating the difference in the first and second conductivitymeasurements to the amount of boron present in the aqueous solution. 38.The method according to claim 37, wherein each of the first and secondboron sensing media comprises at least two hydroxyl groups and at leastone pyrrolic nitrogen.
 39. The method according to claim 37, whereineach of the first and second boron sensing media comprises at least fourhydroxyl groups and at least two pyrrolic nitrogen.
 40. The methodaccording to claim 37, wherein each of the first and second boronsensing media comprises pyridoxine or a derivative thereof.
 41. Themethod according to claim 37, wherein the amount of boron detected andquantified is less than 1 ppb.
 42. The method according to claim 41,wherein the amount of boron detected and quantified is less than 1 ppt.43-46. (canceled)
 47. The boron removal medium according to claim 13,wherein the at least one hydroxyl group is directly attached to the atleast one nitrogenous group.
 48. The method according to claim 37,wherein the at least one hydroxyl group is directly attached to the atleast one nitrogenous group.